Fuel supply system for jet propulsion engines



y 2, 1967 s. R. TYLER 3,316,712

FUEL SUPPLY SYSTEM FOR JET PROPULSION ENGINES Filed Oct. 14, 1965 2 Sheets-Sheet 1 103 101 706 13 FIG/- INVENTQR s-rnmzy E TYLE BY M/hM ATTQRNE? May 2, 1967 s. R. TYLER 3,316,712

FUEL SUPPLY SYSTEM FOR JET PROPULSION ENGINES Filed Oct. 14, 1965 2 Sheets-Sheet 2 lNvENToR STAB/LE y K. TyLErQ ATTORNEY United States Patent 3,316,712 FUEL SUPPLY SYSTEM FUR JET PROPULSION ENGINES Stanley R. Tyler, Cheltenham, England, assignor to Dowty Fuel Systems Limited Filed Oct. 14, 1965, Ser. No. 495,802 Claims priority, application Great Britain, Oct. 20, 1964, 42,762/ 64 7 Claims. (Cl. 6039.28)

This invention relates to fuel supply systems for jet propulsion engines, and it provides a control which is especially suitable for regulating the supply of fuel to each of a number of sets of burners in a reheat system of a gas turbine engine.

According to the invention, a fuel supply system for two or more sets of burners in a jet propulsion engine having a common source of fuel under pressure, comprises flow control means operable to vary the fuel flow from the source, a number of rotary positive fluid displacement devices, one for each set of burners, arranged between the common source and the respective sets of burners, the displacement devices being mechanically interconnected to maintain a fixed proportionality of fluid displacement through said devices, and valve means capable of isolating the fuel source from the, or each, set of burners subsequent to the set to which fuel is first supplied, the valve means being operable, in the case of one set of burners controlled by said valve means, at an increased value of fuel flow to supply fuel from the source to the said set of burners or, in the case of more than one set of burners, controlled by said valve means, at successively increased values of fuel flow to supply fuel from the source successively .to the said sets of burners, whereby the fuel flow to all the sets of burners in use is divided between the sets in proportion to the volumetric capacities of the respective fluid displacement devices.

One embodiment of the invention is illustrated in the accompanying drawings, of which:

FIGURE 1 is a circuit diagram of a reheat system for a gas turbine engine, and

FIGURE 2 is a diagrammatic drawing, partly in section, of some parts of the system which form an assembly.

The reheat system includes three afterburner galleries 11, 12 and .13 which are mounted within the engine duct. Each gallery supplies a set of fuel burners.

The supply of fuel is from a variable delivery pump 14, through a common delivery conduit 15, and three branch conduits 16, 17 and 18 which lead to the respective galleries. Vane motors 2'1, 22 and 23, forming rotary positive fluid displacement devices, are interposed in the respective branch conduits 16, 17 and 18 and their rotors are interconnected by a common shaft 19. The fluid displacements of the motors 21, 22 and 2 3 are determined so as to be capable of maintaining a fixed proportionality of fluid displacement to the respective galleries.

The supply of fuel from the pump 14 is controllable over a wide flow range, and to avoid under-fuelling or over-fuelling of the afterburners, the flow of fuel to each of the galleries is kept within a proportionately smaller range. To this end, it is arranged that over the controlled fuel fiow range from the pump 14, the fuel will be delivered first from the gallery 11, then from both galleries .11 and 12, and finally from all three galleries 11, 12 and 13.

The fuel flow control means regulating the supply of fuel to the portion of the delivery conduit 15 which opens into the branch conduits 16, 17 and 18 will now be described.

The variable delivery pump 14 is of the centrifugal type in which the supply of liquid from an inlet pipe 24 to the eye of the pump rotor 25 is variably throttled by a valve member 26 which is movable with respect to a seat 27. The position of the valve member 26 is determined jointly by a spring 28, and by a servomotor of the kind having a piston 29 which is movable in a cylinder 31 under fluid pressure acting across a fixed restrictor 32, the flow of fluid being controlled by a variably restricted orifice 3 3. The fiuid pressure for actuating this and other servo devices of the system is obtained from the delivery conduit 15 which is connected to a servo pressure line 34 through a non-return valve 35. This line 34 is also supplied with pressure through a non-return valve 36 from the pump 37 which supplies the main burners of the engine, so that a source of servo pressure is available when reheat is selected, at which time there will be no delivery pressure from pump 14. A low pressure vent pipe 49 is shown on the right hand side of FIGURE '1.

Reheat is selected by a device shown, for ease of understanding, as a cam 38 which is turned about a pivot 39 by a control lever 41, and a cam-following plunger 42 which slides in a valve housing 43. A reheat demand signal is provided by the pressure difference in two pipes 44 and 45 leading from the selector device, this pressure difference being derived from the position of the plunger 42 and from a variable presure fluid source, supplied at pipe 46.

The pipe 46 has one flow path through an orifice 47 which is varied by a tapered needle 48 on the end of the plunger 42, and through a fixed orifice 49 in series therewith to a vent 50, the signal pipe 44 leading from between the orifices 47 and 49. A second flow path is provided to the vent 50 through two fixed orifices 5,1 and 52 in series, the signal pipe 45 leading from between the orifices 51 and 52.

When the lever 41 is turned through its full range to the position 41C, the tapered needle 48 progressively reduces the restriction of the orifice 47 so that the pres sure difference in the pipes 44 and 45 increases. The variable pressure source supplied at pipe 46 may be compressor delivery pressure, and since this varies substantially in accordance with air mass fiow through the engine, the maximum fuel flow demand signal selectable by the lever 41 will be substantially proportional to the air available for combustion. The lever 41 thus provides, between its position 41 and 41C, full range reheat control under varying engine-operating conditions.

The plunger 42 has a tapered portion arranged to close a switch 53 at the position 41A of the lever, and to close a switch 54 at the position 41 B of the lever. The function of these switches will subsequently be referred to.

The pressures in the pipes 44 and 45 act in bellows 55 and 56 of a flow-metering device 57. This device has a lever 58 pivoted at 59, one arm of the lever passing between the bellows 55 and 56 and the other arm of the lever passing between springs 61 and 62. The spring 61 reacts against a fixed seating, while the spring 62 reacts against one end of a movable valve spool 63. The other end of the valve spool 63 is loaded by a spring 64. The valve bore 65 has annular recesses 66 and 67 interposed in the run of the delivery conduit 15 and arranged so that upward movement of the spool 63 increasingly throttles the fuel flow through the recess 66 to the recess 67.

The lower end of the spool 63 has a servo-piston 68 working in an enlarged bore 69. The piston 68 has a fixed orifice 71 therein exposed on one side to servo pressure from the line 34, and leading from its other side through a pipe 72 to an orifice 73, this orifice being varied by a half ball 74 seated on that arm of the lever 58 which passes between the bellows 55 and 56. The pressure in the conduit 15 upstream of the valve recess 66 is led by a pipe 75 to one side of a diaphragm 77 in a pump flow governor device 76, while pressure in the valve recess 67 is led by a pipe 78 to the other side of the diaphragm 77 against which a spring 79 also acts. The diaphragm 77 acts through a rod 81 on a half ball 82 which is seated against the orifice 33. The discharge side of the orifice 33 is connected by a pipe 83 to the vent pipe 40.

It is seen that the diaphragm 77 senses the pressure drop in the conduit 15 across the flow-metering device, and by its action on the half ball 82 regulates the position of the servomotor piston 29 controlling the inlet valve 26, 27. If, at a fixed setting of the control lever 41 and constant pressure at 46, the flow through the device 57 increases, the increased pressure acts on the diaphragm 77 to decrease the load of the half ball 82 on the orifice 33, so that the servo piston- 29 moves in the direction to close the pump inlet valve 26, 27. The pump delivery is reduced until the pressure drop across the diaphragm i restored. Conversely, a fall in pressure across the flow-metering device 57 increases the pump delivery to restore the pressure drop.

If the reheat fuel flow demand is increased, the restriction of the orifice 47 by the tapered needle 48 is reduced so that pressure in the bellows 55 increases. This reduces the load of the half ball 74 against the orifice 73 so that flow of servo liquid across the orifice 71 and through the pipe 72 increases. The pressure drop across the piston 68 accordingly increases whereby the latter moves to a new position of equilibrium in which the spring 64 is more compressed. The spool 63 thus moves to increase the opening of the annular recess 66, so that the pressure drop across the flow-metering device 57 is then restored by the action of the flow governor device 76 in increasing the pump delivery. Conversely, a reduction in reheat fuel flow demand causes a decrease in opening of the annular recess 66, and a consequent decrease by the governor device 76 of pump delivery.

-It will follow by similar reasoning that an increase in compressor delivery pressure at the pipe 46 will cause an increase in the governed pump flow, while a decrease in such pressure will cause a decrease in the governor pump flow.

The delivery conduit 15 extends from the flow-metering device 57 to the branch conduits 16, 17 and 18 through the main valve 84 of a maximum fuel-flow-limiting governor device which will subsequently be described. This device depends for its control on a flow-metering-valve 85 which is interposed in the branch conduit 16.

A by-pass 86 having a relief valve 87 therein i connected between the downstream side of the valve 85 and the upstream side of the vane motor 21. A return flow by-pass 88 with a relief valve 89 is also provided across the vane motor 22, and another return flow by-pass 91 with a relief valve 92 across the valve motor 23. Shutofl valves 92 and 93 are interposed in the branch conduits 17 and 18 respectively, between the by-pass connections and the galleries. The valve 92 has a movable valve member 94 of differential area comprising a smaller diameter piston 95 which is acted upon continuously by servo pressure from the line 34. A branch 96 from the line 34 leads to the vent pipe by way of a fixed restrictor 97 and a solenoid-operated pilot valve 98. Between the restrictor 97 and the valve 98, the branch 96 is connected to one side of a larger diameter piston 99 of the valve member 94. The pilot valve 98 i normally closed against the fluid pressure in the branch pipe 96 by a spring 101, whereby the fluid pressures acting on the larger diameter piston 99 and the smaller diameter piston 95 are equal. The main valve member 94 is thus maintained in its left-hand position closing the outlet 102 leading to the gallery 12. The valve 92 is opened by the energising of the coil leads 103 of the solenoid-operated pilot valve 98 caused by closure of the switch 53, whereupon the fluid flow through the restrictor 97 to the vent pipe 40 causes a drop in pressure acting on the large diameter piston 99, so that the main valve member 94 moves to the right and opens the valve 92. The shut-off valve 93 is similar in construction to the valve 92 and it has a fixed restrictor 104 and a solenoid-operated pilot valve 105 associated therewith, the latter having coil leads 106 energized by closure of the switch 54. The pilot valves 101 and 105 and the shut-off valves 92 and 93 constitute valve means controlling the admission of fuel to the galleries 12 and 13.

When fuel flow from the pump 14 is started by turning the control lever 41 from the full line position shown, all the fuel delivered to the conduit 15 flows through the branch conduit 16 to the gallery 11 because the switches 53 and 54 are open and the shut-off valves 92 and 93 are accordingly closed. The vane motor 21 will turn and drive the vane motors 22 and 23, but because the shut-off valves 92 and 93 are closed, the fuel displaced by the vane motors 22 and 23 is recirculated through the relief valves 89 and 92 respectively which operate at low pressure.

At a stage of operation of the flow-control means when the control lever has been advanced to the position 41A, the switch 53 is closed, causing the shut-off valve 92 to open whereby the fuel flow is shared by the branch conduits 16 and 17, and thus by the burner galleries 11 and 12, in the desired proportionality which is determined by the volumetric displacements of the two vane motors 21 and 22. At the position 41B of the control lever, the switch 54 is closed, causing the shut-off valve 93 to open, whereby the fuel flow is shared by the branch conduits 16, 17 and 18, and thus by the burner galleries 11, 12 and 13, again in the desired porportionality.

Thus, before the fuel flow from the burners of the gallery 11 can rise to a value at which there would be overfuelling, that is the presence of unburnt fuel in the gas stream past the burners, the flow is reduced by bringing the gallery 12 into use. Before the fuel flow from the burners of both galleries can rise to a value at which there would be over-fuelling, the flow in both galleries 11 and 12 is reduced by bringing the gallery 13 also into use.

At or about the position 41C of the control lever, the maximum fuel flow to the galleries 11, 12 and 13 can be limited by the governor device now to be described, this governor being provided as an additional safety-measure. The flow-metering valve 85 has a spring-loaded valve member 111 co-operating with an orifice 112 to provide a pressure difference in the upstream pressure take-off pipe 113 and the downstream pressure take-off pipe 114 which is a signal of fuel flow.

The main valve 84 is controlled by a servo valve unit 115 which has a valve spool 116 movable in response to change in the pressure dilference in the pipes 113 and 114, and to change in compressor delivery pressure which acts in a bellows 117. The unit 115 has connections to the servo pressure line 34 and to the vent pipe 40 enabling the pressures in these pipes to be connected reversably to two service pipes 118 and 119 upon movement of the valve spool 116 through its neutral position. The main valve 84 has a spool 121 which, under servo pressure in the service pipe 119, moves to close a port 122 through which fuel in the delivery conduit 15 flows, and to open a port 123 leading to the vent pipe 40, the flow through the port 123 being limited by restricted orifices 124 provided, for instance, in the spool 121. The main valve member 121 is therefore movable to restrict the flow to the galleries 11, 12 and 13 further by venting part of the flow to pipe 40. It will be seen that the servo valve unit 115 compares the flow signal in the pipes 113 and 114 with the air mass flow as signalled to the bellows 117, and adjusts the spool 121 accordingly.

Servo pressure in the service pipe 118 moves the spool 121 in the direction to open the port 122 and to close the vent port 123.

The governor device described acts in response to the fuel flow through the vane motor 16 and therefore prevents overfueling when the gallery 11 alone is in use. Since the flows to the other galleries, when in use, bear a fixed proportionality to the flow to the gallery 11, the governor device will also prevent overfuelling when the galleries 11 and 12 are in use, and when all three galleries 11, 12 and 13 are in use.

In an alternative embodiment, the maximum fuel flow may be controlled by a centrifugal governor driven by the shaft 19 and shown in broken line at 125, the governor operating a valve 126 which provides a pressure signal in the pipes 127, 128 equivalent to that in the pipes 113, 114.

The relief valve 87 has a regulating function at the transition stage of opening the shut-off valve 92. At first, the gallery 12 will be empty and offer no fluid flow resistance with the result that the vane motor 22 will tend to race and drive the vane motor 21 momentarily at increased speed, thereby causing momentary over-fuelling of the gallery 11. However, the blow-off pressure of the relief valve 87 is such that under the momentary increase in fuel pressure downstream of the vane motor 21 it will open sufficiently to recirculate the excess flow, thereafter closing when the gallery 12 is full of fuel and correct running of the vane motor 22 has been achieved. When the control lever in position 41B closes the switch 54 to open the branch conduit 18 to the gallery 13, both relief valves 87 and 89 for the vane motors 21 and 22 can momentarily open if the vane motor 23 tends to race.

The relief valve 87 will also open if the burner gallery 11 becomes partially blocked, for example by a carbon deposit, so that part of the fuel flow through the device 21 will be recirculated and the rotors of all the devices 21, 22 and 23 will continue to turn together. Moreover, the correct functioning of the flowmetering valve 85 will not be substantially affected because the by-pass 86 is connected downstream of the valve 85.

The branch conduits 16, 17 and 18 include non-return valves 106, 107 and 108 which prevent the risk of blowback of combustion products into the fuel system, in the case of engine malfunction, and they also help to keep the branch conduits primed with fuel upstream of the non-return valves.

In the unitary assembly of FIGURE 2, parts as so far described bear the same reference numerals. The servo valve unit 115, the main valve unit 84, and the vane motors 21, 22, 23 constitute an assembly having a common housing 131. The rotor shaft 19 of the vane motors drives a gear train consisting of a drive pinion 132 on the shaft 19, an idler pinion 133, a pinion 134 for rotating the main valve spool 121, and a pinion 135 for rotating the servo valve spool 116. This reduces axial friction of the spools 116 and 121. The pinion 134 is mounted on a stub shaft 136 having a skirt with longitudinal slots 137 which form guideways for rollers 138 carried by the main spool 121 so that the latter can slide and turn.

The sliding movement of the spool 116 is less and is accommodated by overlap of the pinions 134 and 135 which remain in mesh.

The bellows 117, opposed by an evacuated bellows 139 acts on one end of a pivoted lever 141, the other end of the lever being loaded against the spool 116 through a thrust bearing 142. An adjustable spring 143 also acts through a thrust bearing 144 against a rotatable extension 145 of the spool 116.

I claim as my invention:

1. A fuel supply system for at least two sets of burners in a jet propulsion engine, a flow-control member and flow-control means operable thereby over a range of movement of the flow-control member to vary fuel fiow from a source to a delivery conduit, a branch conduit connecting the delivery conduit to each set of burners, a rotary positive fluid displacement device interposed in each branch conduit, all such fluid displacement devices having interconnecting drive means to ensure rotation of said devices in unison, valve means including an openable and closable shut-off valve disposed in the branch conduit which is connected to a set of burners subsequent to a first set of said sets of burners, and valve-control means adapted for operation by said flow control member and acting on said valve means, when the flow-control member is moved through an intermediate position in its range of movement in the flow-increasing sense, to open the shut-off valve and, when the flow-control member is moved through said intermediate position in the flow-decreasing sense, to close the shut-off valve, the fluid-displacement devices maintaining a fixed proportionality in the fuel flows to the respective sets of burners in use when the shut-off valve is open.

2. A fuel supply system according to claim 1, wherein the shut-off valve is interposed in the branch conduit between the fluid-displacement device and the set of burners, and wherein a by-pass passage is provided across the fluid displacement device enabling fuel to be recirculated through said device when the shut-off valve is closed and the fluid displacement device in the branch conduit to the first set of burners is rotated by the passage of fuel therethrough.

3. A fuel supply system according to claim 2, wherein the bypass passage has its inlet for fuel connected to the branch conduit at a position between the fluid displacement device and the shut-off valve, and wherein a relief valve is interposed in the by-pass passage.

4. A fuel supply system according to claim 1, wherein the flow-control means includes a flow-selecting device which is responsive both to a signal of a variable engineoperating condition and to the position of an element which is movable by the flow-control member, said device being operable to provide a flow-controlling signal to which the flow-control means responds which is variable by said element, for each value of engine-operating signal, over the full range of movement of the flow-control member.

5. A fuel system according to claim 1, including a flowmeasuring device interposed in the branch conduit supplying the first set of burners, and a maximum fuel flow governor having a flow-limiting valve in the delivery conduit, the governor including means responsive to a signal of fuel flow from the flow-measuring device and to a signal of an engine-operating condition to provide an upper limit to fuel flow through the fluid displacement device to the first set of burners, and therefore through the interconnected fluid displacement device to the next set of burners when the shut-ofi valve is open.

6. A fuel supply system according to claim 5, wherein the flow-limiting valve comprises an axially movable spool having a rotary driving connection from the fluid displacement devices, to reduce frictional resistance to axial movement of the spool.

7. A fuel supply system according to claim 1, including a centrifugal governor device having a rotary driving connection from the fluid displacement devices, a valve operable by the centrifugal governor device to provide a signal of the rotational speed of said fluid displacement devices, and a maximum fuel flow governor having a flowlimiting valve in the delivery conduit, the governor including means responsive to said signal or rotational speed and to a signal of an engine operating condition, and acting at each engine-operating condition to provide an upper limit to rotational speed of the fluid displacement devices.

No references cited.

JULIUS E. WEST, Primary Examiner. 

1. A FUEL SUPPLY SYSTEM FOR AT LEAST TWO SETS OF BURNERS IN A JET PROPULSION ENGINE, A FLOW-CONTROL MEMBER AND FLOW-CONTROL MEANS OPERABLE THEREBY OVER A RANGE OF MOVEMENT OF THE FLOW-CONTROL MEMBER TO VARY FUEL FLOW FROM A SOURCE TO A DELIVERY CONDUIT, A BRANCH CONDUIT CONNECTING THE DELIVERY CONDUIT TO EACH SET OF BURNERS, A ROTARY POSITIVE FLUID DISPLACEMENT DEVICE INTERPOSED IN EACH BRANCH CONDUIT, ALL SUCH FLUID DISPLACEMENT DEVICES HAVING INTERCONNECTING DRIVE MEANS TO ENSURE ROTATION OF SAID DEVICES IN UNISON, VALVE MEANS INCLUDING AN OPENABLE AND CLOSABLE SHUT-OFF VALVE DISPOSED IN THE BRANCH CONDUIT WHICH IS CONNECTED TO A SET OF BURNERS SUBSEQUENT TO A FIRST SET OF SAID SETS OF BURNERS, AND VALVE-CONTROL MEANS ADAPTED FOR OPERATION BY SAID FLOW CONTROL MEMBER AND ACTING ON SAID VALVE MEANS, WHEN THE FLOW-CONTROL MEMBER IS MOVED THROUGH AN INTERMEDIATE POSITION IN ITS RANGE OF MOVEMENT IN THE FLOW-INCREASING SENSE, TO OPEN THE SHUT-OFF VALVE AND, WHEN THE FLOW-CONTROL MEMBER IS MOVED THROUGH SAID INTERMEDIATE POSITION IN THE FLOW-DECREASING SENSE, TO CLOSE THE SHUT-OFF VALVE, THE FLUID-DISPLACEMENT DEVICES MAINTAINING A FIXED PROPORTIONALITY IN THE FUEL FLOWS TO THE RESPECTIVE SETS OF BURNERS IN USE WHEN THE SHUT-OFF VALVE IS OPEN. 